Re: preempt-rt, NUMA and strange latency traces

Sébastien Dugué
2006-02-10T13:16:56Z

On Thu, 2006-02-09 at 15:02 -0500, Lee Revell wrote:
> On Thu, 2006-02-09 at 12:24 +0100, Sébastien Dugué wrote:
> > On Thu, 2006-02-09 at 01:04 -0500, Lee Revell wrote:
> > > On Wed, 2006-02-08 at 11:45 +0100, Sébastien Dugué wrote:
> > > > The more I think about it, the more I tend to believe it's hardware
> > > > related. It seems as if the CPU just hangs for ~27 ms before
> > > > resuming processing.
> > >
> > > That would be an exceptionally long latency - you would probably notice
> > > it if the mouse froze, VOIP dropped out, ping stops, etc for 30ms.
> > >
> >
> > It's a test machine and I use it remotely with console redirected so
> > no mouse, no RT applications aside from my silly nanosleep() loop. But
> > I do notice that that test sometimes takes more time (ie when I get
> > those weird latencies).
>
> Argh. You would think the vendors would consider a 30ms delay
> unacceptable. This is big enough to show up on an MRTG graph of ping
> times ferchrissake.
>
> I guess the assumption is that most hardware will never be used for even
> soft RT work...
>
> Lee
>

That may be but in that case I may be pushing it a bit far testing
that kind of box with realtime stuff.

As a former hw designer I find it useful to have some hardware
monitoring capabilities on a system but it should either not be so
intrusive or at least we should be able to disable it.

Sébastien.